1. Field of the Invention
The present invention relates to power supply control systems for controlling two or more power supplies coupled to a common load.
2. Description of the Prior Art
In a previously proposed arrangement the outputs from two individual power supplies are connected to supply a common load with power. This is done to feed the load with more current than a single power supply can provide or to provide a back-up in the event that one of the two power supplies fails.
When constant voltage DC power supplies are used and because of the tolerances to which power supplies are manufactured, the precise output voltages of the two supplies will rarely be exactly the same. As a result when the two power supplies are connected to a common load the supply with the marginally higher output voltage will tend to supply the lion's share of current, leaving the other power supply virtually idle.
Such a condition is undesirable since the power supply with the slightly higher output voltage will tend to operate at the limit of its capacity and so will be subject to greater stress and therefore liable to earlier failure. Also because the other power supply tends to be idle it is difficult to detect when it fails until it is called upon to take over from the active power supply at which time it is too late to take corrective action.
Furthermore if the active power supply fails then 100% of the load is immediately transferred to the idle supply. This is likely to cause a significant transient effect on the output voltage during the change-over period and thus is undesirable. Such transient effects are significantly reduced if both supplies share 50% load prior to one supply failing and during the subsequent transfer of the 50% load to the remaining supply.
It is an object of the present invention to provide an improved power supply control system.